When asked to draw a scientist, less than one per cent of children in the 1960s and 1970s drew a woman. This rose to 28% between the 1980s and present day.

However, children are still far more likely to draw a traditionally male figure when asked to depict a scientist.

Image copyrightVasilia ChristidouImage caption
Children tend to depict scientists in lab coats and with technical equipment

"The effect ... increased over age as children became more connected to their world and became more aware of the male dominance of science," Prof Alice Eagly, a co-author on the study, told BBC News.

"The fact that children are still drawing more male than female scientists reflects their environment," said David Miller, the study's lead author. "Given the underrepresentation of women we observe in several science fields, we shouldn't except equal numbers. Encouragingly though, we can see that children's stereotypes change over time."

Despite women's representation in science improving significantly since the 1960s, girls draw on average 58% of scientists as men, with boys drawing 96%.

Yet, the study highlights, by 2013 women were 49% of biological scientists, 35% of chemists, and 11% of physicists and astronomers in the United States.

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Only 28 girls, of nearly 5,000 children surveyed in the 1960s and 1970s, drew women scientists.

Bianca Reinisch of the Free University of Berlin, who was not involved in the study, cautions that the way in which children are prompted to draw for the study may also be changing.

"Although it is true that studies make use of the prompt "Draw a scientist,", there are differences in the setting of the assessments and even variations of the prompt," she explained. Children's responses could be influenced by posters visible in the room or the way in which the task is phrased to them.

Prof Eagly points out that the exercise is not perfect, yet it is a useful indirect measure as it can encourage children to share their thoughts and ideas on a topic without realising they are being tested.

The authors suggest that media stereotypes play a significant role in children's images of scientists as they get older. Where it was possible to determine detailed characteristics, many of the scientists in the drawings wore lab coats and glasses. On average, 79% were Caucasian.

Image copyrightVasilia ChristidouImage caption
A scientist, as drawn by a 10 - 11 year old girl in Greece

It is also notable that the the test requires figures to be indentified as one of two genders. Although the Northwestern analysis factors in figures of "indeterminate" gender, Bianca Reinisch considers that some earlier studies may have been "forced" to choose between the categories of men and women when assessing the pictures.

When children in one study were also asked to draw a teacher, only a quarter drew men, suggesting that gender stereotypes persist across other professions.